1. Field of the Invention
The present invention relates to a radio receiver having properties desirably set according to an external CPU (Central Processing Unit).
2. Description of the Related Art
Generally, radio receivers have functional circuits, such as an RF-AGC circuit for maintaining an RF signal at a constant level according to an RF signal, an IF-AGC circuit for maintaining an RF signal at a constant level according to an IF signal, a station detection circuit for detecting presence of a broadcasting station in response to a receiving field strength equal to or more than a predetermined level, and other functions. These functions are effected based on the result of comparison between a signal level of a control object and a reference voltage. Functions to he effected based on such a comparison result is not limited to the above circuits, and may include various other circuits.
FIG. 3 shows a radio receiver including a circuit for receiving reference value data generated by a control circuit of an external CPU, and for setting a reference voltage according to the reference value data. When reference value data is transferred in series from an external CPU 1 to the radio receiver circuit 2, the reference value data is taken into a data input/output circuit 3, and the circuit 3 then outputs a control signal to, for example, a station detection circuit 4 according to the data. The station detection circuit 4 comprises a comparison circuit 5, resistors with resistance values R, 2R, 4R, and 8R, respectively, and transistors TR1 to TR4 respectively connected to the resistors. By turning on or off the transistors TR1 to TR4 in response to a control circuit, combination of the resistors R to 8R can be desirably changed so that a reference voltage can be changed depending on the combinations.
Here, in the circuit shown in FIG. 3, the data input/output circuit 3 applies a control signal for determining a reference signal to not only the station detection circuit 4, but also to an application circuit 6, such as an RF-AGC circuit, an IF-AGC circuit, or the like. That is, increase of the number of circuits requiring a reference voltage increases the number of resistors, such as a station detection circuit 4, and transistor elements, resulting in a problem such that the number of control signals to control the transistor, and thus the number of signal lines for control signals in the radio receiving circuit 2, is increased.
The present invention has been conceived to overcome the above problems and aims to provide a radio receiver for receiving electric waves from a broadcasting station, comprising a heterodyne radio receiving circuit; a frequency control circuit for controlling frequency of a local oscillation signal applied to the radio receiver in accordance with frequency data; and a control circuit for outputting the frequency data in accordance with a receiving frequency, wherein the control circuit supplies reference data to the frequency control circuit, the reference data corresponding to a reference voltage used in a different circuit in the radio receiving circuit, the frequency control circuit includes a reference voltage generation circuit for converting the reference data into reference voltage to supply to the different circuit in the radio receiving circuit.
Also, the different circuit in the radio receiving circuit may be an IF-AGC circuit.
Further, the different circuit in the radio receiving circuit may be a broadcasting detection circuit.
Still further, the control circuit may combine frequency data and reference value data, and outputs resultant data as serial data.
Yet further, the frequency control circuit may also include a latch circuit for latching the serial data supplied, so that the latched data is divided into frequency data and reference data.
Yet further, the radio receiving circuit and the frequency control circuit may be integrated on a single semiconductor substrate so that a local oscillation frequency is controlled on the substrate and a reference voltage converted is applied to the different circuit in the radio receiving circuit.
According to the present invention, reference data, as well as frequency data, is applied to a frequency control circuit for conversion therein into reference value data to be applied as a voltage signal to an application circuit of a radio receiving circuit. That is, the application circuit is coupled with only one voltage signal line.